This invention pertains to particular cyano-substituted tertiary amines as catalysts for the formation of urethane polymers by the reaction of organic isocyanates with active hydrogen-containing compounds.
It is well known to the art that urethane polymers are provided by the reaction of organic polyisocyanates and active hydrogen-containing organic compounds, usually in the presence of one or more activators, and that blowing action is provided when cellular products including flexible, semi-flexible and rigid foams, are desired. It is also known that a number of different chemical reactions occur during polymer formation and expansion. For example, in addition to the chain-extending, urethane-forming reaction between free isocyanate groups and active hydrogen, initially formed urethane linkages bearing secondary hydrogen may also function as a source of active hydrogen and react with additional isocyanate to form cross-links between polymer chains. Further, in water-containing systems such as those employed for the manufacture of flexible foams, isocyanate is also consumed by reaction with water, thereby generating carbon dioxide blowing agent in situ and introducing urea groups. The nature of the cellular structure and the physical and mechanical properties of the foam are influenced by the extent of such reactions, and the relative rates and point in time at which they occur. Although balancing these variables so as to achieve a particular type or grade of foam can be controlled to some extent by the functionality, molecular weight and other structural features of the polyisocyanate and active hydrogen-containing reactants, the catalyst system also plays a significant role in this respect.
Among the relatively few compounds that have achieved widespread commercial application as catalysts in polyurethane manufacture are: tertiary amines consisting of carbon, hydrogen and nitrogen, as typically illustrated by 1,4-diazabicyclo[2.2.2]octane ("triethylenediamine") and N,N,N',N'-tetramethyl-1,3-butanediamine; and tertiary amines consisting of carbon, hydrogen, nitrogen and oxygen wherein oxygen is present as ether oxygen, as typically illustrated by bis[2-(N,N-dimethylamino)ethyl]ether and N-ethylmorpholine.
A relatively recent advance in the area of flexible polyurethane foam technology which has triggered intensive research effort to develop improved activators, is the advent of reaction mixtures having a sufficiently high reactivity to provide more complete reactions during polymer formation and expansion, thereby eliminating the need in commercial practice to post-cure the foam at high temperatures (300.degree.-500.degree. F.) to obtain a product of satisfactory overall properties. In addition to the saving in cost which elimination of high temperature post-curing offers to the foam manufacturer, such highly reactive formulations also provide flexible foams of generally improved flammability characteristics, more linear and thus improved load/deflection properties, low flex fatigue, and greater resiliency. In view of this latter characteristic, such products are referred to generally as high-resilience foams. In view of the aforesaid combination of properties, high-resilience foam is particularly suited as cushioning material in automotive interiors. In the production of at least a substantial proportion of high-resilience foam being manufactured at the present time, the aforementioned N-ethylmorpholine is used as a major component of mixed catalyst systems.
With respect to flexible polyurethane foam manufacture generally, it is often the preferred practice of foam manufacturers to premix the amine catalyst(s), water and foam stabilizer(s) and to feed the aqueous premixture, commonly referred to as the activator stream, to the foam formulation as a single stream. It is often observed, however, that the mere mixing of the amine and foam stabilizing components in water forms a highly viscous mixture which detracts from the processing advantage of adding these components as a combined stream rather than as individual streams. This problem is encountered in particular in the manufacture of polyester polyol-based polyurethanes in which silicon-free organic surfactants are used to stabilize the foam. Thus, when certain otherwise catalytically effective amine catalysts such as bis-[2-(N,N-dimethylamino)ethyl]ether, are present in combination with organic foam stabilizers, the activator stream becomes extremely viscous, approaching or actually undergoing gellation, thereby hampering or preventing pumping. In this respect, N-ethylmorpholine is also used with advantage in the manufacture of polyester-polyol based foams in that it is suitably employed as an amine component of aqueous activator streams containing organosilicone or silicon-free organic foam stabilizers.
The usefulness of N-ethylmorpholine in the manufacture of cellular urethanes, however, is attended with certain disadvantages. Thus, N-ethylmorpholine suffers the very serious drawback of having a particularly strong amine odor. The large quantities of N-ethylmorpholine which are employed relative to other catalyst components of the foam formulation causes an obnoxious atmosphere at and surrounding the foam manufacturing plant site and also provides foams having a strong residual amine odor. This compound is also associated with a number of serious toxic effects; see, for example, Plastics Technology, "Catalysts Improve As Their Need Increases" pages 47-49 (July 1972). Consequently, it is desirable and is a primary objective of this invention to provide a direct replacement for N-ethylmorpholine in the production of cellular polyurethanes and thereby allow for at least a substantial reduction in the relatively large amounts presently employed. Various other objects and advantages of the present invention will become apparent from the accompanying description and disclosure.